1. Field of the Invention
The present invention relates to an information-processing device, an information-processing method, and an information-processing program product that transmits a variety of content needed to achieve copyright protection.
2. Description of the Related Art
With dissemination and digitalization of computer network in recent years, products, called as digital information electric appliances, are widely spread in use. Further, with start of ground wave digital broadcasting service, digital broadcasting-compliant televisions, STB (Set Top Box) and DVD recorders are predicted to become further widespread in the future. If these digital electric appliances are connected over a network, users are available to enjoy a variety of content via the home network with a resultant increase in utility value.
As used herein, the term “content” refers to various digital data, involving moving image data, such as MPEG2 and MPEG4, and audio data, and in addition to these, document data such as text data and still image data. Content composed of this kind of digital data is advantageous in that it can be easily copied without deteriorations, and then again, attention needs to be paid for copyright of content.
It is preferable that an area available for exchanging content, whose copyright is to be protected, is limited to a certain range, for instance, an area under a legitimate authority such as an area for private use defined under the Copyright Act or a further narrowed area. It is preferable for content to be restricted from exchanging with a third party in an area beyond such a limited range.
In the event of transmitting AV data on IP (Internet Protocol), IP has a capability of transmitting data without any physical restrictions in a cable length. Therefore, issues easily occur on a copyright law. That is, in IP, technology, a so-called VPN (Virtual Private Network) in which IP networks can be logically connected to one another in remote areas, becomes widely used. By such technology, for example, it enables to logically connect equipment in a home network of Mr. X's residence in a district A with equipment in another home network of Mr. Y' residence in another district B (physically remote from the district A) for transmitting AV data. For this reason, content in the Mr. X's residence is not closed within the home network of Mr. X's residence. Then, Mr. Y in a remote place can browse content on the network owned by Mr. X by connecting the Mr. Y's home network to Mr. X's home network.
As technique of addressing such an issue, it is conceived to measure a round trip time (RTT) between a transmitter and a receiver. The RTT is time between a time instant at which a signal is transmitted from one unit and another time instant at which the one unit to receive a reply signal from the other unit transmitting the replay signal in response to the transmitted signal.
Only under a situation where the round trip time between the transmitter and the receiver is not greater than a threshold value, the transmitter and the receiver are regarded to be present within a fixed range in terms of a distance upon which the data transmission is permitted, while preventing the data transmission and reception from remote places.
However, in the case where the round trip time is applied for the limitation, a condition of network traffic spreads the round trip time. Repeat measuring the round trip time for every transmission of data raises a problem that the transmission of data has been terminated until the round trip time is not greater than the threshold value. Therefore, another technique is proposed. In the technique, a list, which includes a datum for a receiver passing a test of the round trip time, is provided for a certain period, then the listed receiver transmits data without measurement of the round trip time, and a non-listed receiver transmits data after measurement of the round trip time. However, two problems arise in the technique. The technique requires a nonvolatile random access memory (RAM) so as to store an accumulated amount of time for transmission of the data from the transmitter even after abnormal end, such as a shut down. For the purpose of storing the accumulated amount of time accurately from a viewpoint of copyright protection, it is preferable that the accumulated amount of time is stored in the nonvolatile RAM fully. However, frequent writing of data for the accumulated amount of time in the nonvolatile RAM shortens a lifetime of the nonvolatile RAM. This is the first problem.
In the case of measuring an accumulated amount of transmitted data instead of time, there are various durations for holding the list in accordance with bit rate, such as low bit rate content, for example, audio data, or high bit rate content, for example, high-definition moving image data. Therefore, it is hard to predict that the accumulated amount of time approaches the limitation, and re-measurement is required for passing the test to transmit next content after the accumulated amount of time exceeds the limitation without re-measurement. The re-measurement preceding the transmission of content prevents quick transmission of the content. Particularly, low frequency of writing for solving the first problem causes extreme increase of amount of time added to the accumulated amount of time. Consequently, the accumulated amount of time may exceed the limitation during transmission of data before the re-measurement. This is the second problem.